The present invention is directed to improvements in article sorting machines. Specifically, the present invention is directed to a method for updating and maintaining zero calibration values representative of the average empty cup weight stored in article sorting machines of the type employing cups to sort articles. The average empty cup weight, also known as the average tare, is employed by the article sorting machine to determine the weight of the article being transported by the cup.
Article sorting machines are known. U.S. Pat. No. 4,106,628 discloses an article sorting machine for sorting articles according to weight. The article sorting machine comprises a plurality of cups connected in a continuous belt for carrying the articles to be sorted. The cups are transported over an electronic weight station which provides a weight signal for each cup transported thereover. The weight signal has a value representative of the weight of the cup carried over the weight station, and if the cup is carrying an article, the weight of the cup and the article.
According to U.S. Pat. No. 4,106,628, electronic circuitry compares the weight signal to a plurality of reference values called weight cutoffs or thresholds set by the operator of the machine. The ranges between successive weight cutoffs define weight breaks. After the article is weighed and classified into a weight break, the cup is transported over a plurality of discharge stations where the article is discharged from the cup at a selected one of the discharge locations depending upon the weight break into which the article has been classified.
The aforementioned patent teaches the use of a potentiometer in the electronic weight scale circuitry to compensate for the weight of the cup. The potentiometer is manually set to provide a reference value which most nearly corresponds to the weight signal provided by the weight scale when an empty cup passes thereover. In this manner, the weight station provides a weight signal compensated for cup weight, depending upon the setting of the potentiometer.
A problem with the aforementioned compensation circuit is that it cannot automatically adjust the value of the reference signal to compensate for the additional weight that an empty cup acquires due to dirt, grime, etc. which accumulates in the cup during a sorting process. Some schemes have been developed to provide such adjustment. For example, in one known scheme, the electronic circuit disclosed in aforementioned U.S. Pat. No. 4,106,628 is replaced with a microcomputer and programmed to perform the hardware functions disclosed therein utilizing well-known programming techniques. The microcomputer is further programmed to sense when an empty cup passes over the weight scale by comparing the value of the weight signal to a reference signal. If the value of the weight signal fails to exceed the value of the reference signal, the microcomputer assumes that an empty cup is present on the weight scale and stores the value of the weight signal corresponding to that cup in a memory location corresponding to that cup. Thus, according to this scheme, a lookup table is provided in a section of memory, and each cup is assigned a location in the lookup table. The computer stores the empty cup weight for each cup in the lookup table. Each time an empty cup passes over the weight scale, the new value of the weight signal replaces the old value stored in the lookup table. However, if a cup carrying an article passes over the weight station, the value of the cup weight stored in the lookup table is used as the tare to compute the weight of the article alone.
One of the drawbacks of the aforementioned lookup table method is that it requires substantial memory and processing time. Thus, one memory location is required for each cup in the machine. The microcomputer is required to, for each cup passing over the weight scale, determine the memory location of the tare value for the cup over the scale, retrieve that value from the lookup table and subtract it from the weight value for the cup and article over the scale. This process is inefficient in terms of processing time.
It is therefore desirable to provide a method for updating and storing values indicative of average tare which requires only minimum memory requirements and requires minimum processing time.